1. Field of the Invention
The invention relates to a gravity axis determination apparatus for determining a gravity axis on the basis of acceleration in each axis and also to a mobile terminal apparatus using the gravity axis determination apparatus.
2. Description of the Related Arts
In recent years, portable mobile terminal apparatuses such as cellular phones and music players that have a display for displaying still images and motion images have widely been spread. Among such terminal apparatuses, there are apparatuses having a function for displaying images in such a way that a direction of a display screen on the display is fixed to a predetermined direction irrespective of whether the terminal itself is placed in the longitudinal direction or in the lateral direction. For example, a mobile terminal apparatus in which a degree of inclination and a direction of the mobile terminal are detected and an image is displayed on a display screen on the basis of a virtual display screen region obtained from the degree of inclination and the direction has been disclosed in Japanese Patent Kokai No. 2000-56893 (Patent Literature 1).
Ordinarily, terminals performing the displaying process have an acceleration sensor for detecting a magnitude and a direction of an acceleration of each of an X axis, a Y axis, and a Z axis and discriminates a direction of gravity on the basis of the acceleration of each axis. A process for obtaining a direction of a gravity acceleration by using the acceleration sensor is also used in a car navigation apparatus or the like which can be classified into the mobile terminal apparatus. For example, Japanese patent kokai No. 11-190743 (Patent Literature 2) discloses a triaxial acceleration detecting apparatus for mounting in a mobile body and which obtains an inclination angle and an inclination direction of the mobile body on the basis of an acceleration in a Z-axis direction and obtains a component in an X-axis direction of a gravity acceleration from the inclination angle and the inclination direction.